About 1 in 10 babies in the United States is born preterm, meaning before 37 weeks of pregnancy. The preterm birth rate held steady at 10.41% in 2024, and it affects some groups disproportionately: Black mothers face a rate of nearly 15%, compared to about 9.5% for white mothers. While not every preterm birth can be prevented, a significant number of them are linked to modifiable factors, and there are specific medical interventions, lifestyle changes, and planning strategies that meaningfully lower the risk.
Know Your Risk Level
The single strongest predictor of preterm birth is having delivered preterm before. If you’ve experienced preterm labor or delivery in a previous pregnancy, your risk is substantially higher this time around. Other major risk factors include carrying twins or triplets, having a short cervix (the lower portion of the uterus that opens during labor), and pregnancies conceived through IVF.
Certain health conditions also raise the risk: chronic high blood pressure, diabetes or gestational diabetes, blood clotting disorders, urinary tract infections, bacterial vaginosis, and placenta previa (where the placenta covers the cervical opening). Being underweight or having obesity before pregnancy, being younger than 18 or older than 35, and having a prior cesarean delivery or uterine fibroid removal all contribute as well.
Some risk factors are outside your control, including race, age, and uterine anatomy. But understanding where you fall on the risk spectrum determines which preventive steps apply to you and how closely your pregnancy should be monitored.
Space Your Pregnancies Appropriately
The interval between pregnancies has a direct effect on preterm birth risk. Research published in the New England Journal of Medicine found that conceiving 18 to 23 months after a previous live birth produces the lowest risk of adverse outcomes, including preterm delivery. Shorter gaps, particularly less than 6 months between giving birth and the start of a new pregnancy, are associated with significantly higher risk. Longer intervals also carry somewhat elevated risk, though the effect is less dramatic. If you’re planning another pregnancy, aiming for at least 18 months between delivery and your next conception gives your body time to fully recover.
Progesterone Therapy for High-Risk Pregnancies
Progesterone is a hormone that helps maintain pregnancy, and supplemental vaginal progesterone is one of the most well-studied interventions for preventing preterm birth. It’s recommended in two specific situations: if you’ve had a previous spontaneous preterm birth, or if a transvaginal ultrasound between 16 and 24 weeks shows your cervix has shortened to 25 millimeters or less. That 25 mm threshold corresponds roughly to the 10th percentile for cervical length at that stage of pregnancy.
This recommendation also applies to twin pregnancies with a short cervix. Progesterone therapy has not been linked to an increase in birth defects or developmental problems in children, which makes it a well-tolerated option. In some cases, progesterone may even be offered as an alternative to cervical cerclage, a surgical procedure where a stitch is placed around the cervix to help keep it closed. Current guidelines suggest that combining progesterone with cerclage or a pessary doesn’t add benefit, so one approach is typically chosen rather than layering them together.
Cervical Monitoring
If you have risk factors for preterm birth, your provider will likely monitor your cervical length with transvaginal ultrasound during the second trimester. The cervix naturally shortens as pregnancy progresses, but it should stay long through most of the second trimester. A measurement under 25 mm between 16 and 24 weeks is considered short and triggers a conversation about intervention, whether that’s progesterone, cerclage, or increased surveillance. This screening is particularly important if you’ve had a prior preterm delivery or cervical surgery.
Low-Dose Aspirin for Preeclampsia Prevention
Preeclampsia, a dangerous rise in blood pressure during pregnancy, is a leading cause of medically necessary preterm deliveries. Low-dose aspirin (81 mg per day) can reduce this risk when started early. It’s recommended for anyone with at least one high-risk factor for preeclampsia: a history of preeclampsia, carrying multiples, kidney disease, autoimmune disease, type 1 or type 2 diabetes, or chronic high blood pressure.
If you don’t have a single high-risk factor but have two or more moderate-risk factors, aspirin is still worth discussing with your provider. Moderate-risk factors include a first pregnancy, being 35 or older, a BMI over 30, and a family history of preeclampsia. The key is timing: aspirin should ideally be started before 16 weeks of pregnancy and continued daily until delivery. Starting after 28 weeks provides little benefit.
Managing Diabetes and Blood Pressure
Chronic conditions that are well controlled before and during pregnancy are far less likely to trigger a preterm delivery. For diabetes, the goal before conception is an A1C under 6.5%, which reduces the risk of preterm birth along with other complications like preeclampsia and birth defects. During pregnancy, the targets tighten: fasting blood sugar under 95 mg/dL and post-meal levels under 140 mg/dL at one hour or under 120 mg/dL at two hours.
For chronic high blood pressure, keeping readings below 140/90 mmHg during pregnancy is the standard recommendation. But there’s strong evidence that aiming lower makes a real difference, especially for women who also have diabetes. In one large trial, women with both diabetes and chronic hypertension who maintained blood pressure below 130/80 had their rate of indicated preterm birth before 35 weeks cut by more than half, dropping from about 20% to 8%. If you have either condition, getting it well controlled before you become pregnant, and maintaining that control throughout, is one of the most impactful things you can do.
Screening for and Treating Infections
Urinary tract infections, including ones with no symptoms at all, are linked to preterm birth. Asymptomatic bacteriuria, where bacteria are present in the urine but cause no noticeable problems, shows up in 2% to 10% of pregnant women. Routine urine screening early in pregnancy catches these silent infections, and treating them has been shown to reduce both kidney infections and preterm delivery. If you’re diagnosed with a UTI during pregnancy, a full course of antibiotics is important, and your provider may recheck your urine afterward to confirm the infection has cleared.
Bacterial vaginosis and trichomoniasis are vaginal infections also associated with higher preterm birth risk. These are typically identified through symptoms like unusual discharge or odor, though bacterial vaginosis can sometimes be subtle. Reporting any changes to your provider allows for early treatment.
Omega-3 Supplementation
DHA, an omega-3 fatty acid found in fatty fish and fish oil supplements, appears to lower preterm birth risk at higher doses. An NICHD-funded clinical trial found that pregnant women taking 1,000 mg of DHA daily had lower rates of preterm birth compared to those taking 200 mg daily. The higher dose seems to work by influencing inflammatory immune responses involved in triggering labor. A typical prenatal vitamin contains far less DHA than 1,000 mg, so a separate supplement may be needed to reach this level. Starting between 12 and 20 weeks of pregnancy aligns with the timeframe studied in the trial.
Workplace and Lifestyle Factors
The physical demands of your job matter more than many people realize. A large meta-analysis found that long working hours increase preterm birth risk by 44%, and shift work raises it by 63%. Jobs involving prolonged standing, heavy lifting, and whole-body vibration (such as operating machinery) add further risk. These physical stressors appear to increase stress hormones and promote uterine contractions while reducing blood flow to the placenta. If your job involves these demands, talking with your provider about modifications or leave options, especially in the second and third trimesters, is worth prioritizing.
Smoking, alcohol use, and drug use during pregnancy all independently raise preterm birth risk and are among the most impactful things to eliminate. Chronic stress and lack of social support are also linked to earlier delivery, likely through similar hormonal pathways as occupational stress. Late or absent prenatal care is another consistent risk factor, not because the visits themselves prevent preterm birth, but because they’re the gateway to every screening and intervention described above. Early and consistent prenatal care is what connects you to cervical monitoring, infection screening, progesterone therapy, aspirin, and blood sugar management at the times when they can actually make a difference.